From on high: Geochemistry of alpine springs, Niwot Ridge, Colorado Front Range, USA
From on high: Geochemistry of alpine springs, Niwot Ridge, Colorado Front Range, USA
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DOI：
10.1002/hyp.13436
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发表时间：
2019-05
影响因子：
3.2
通讯作者：
Jordan F. Fields;D. Dethier
中科院分区：
文献类型：
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作者：
Jordan F. Fields;D. Dethier
美国西部高山地区的融雪泉水和小型（0.5平方公里）高地集水区对输送到下游盆地的水量和无机化学成分做出了重大贡献，但尚未得到广泛研究。矿物风化、运输时间和水文混合控制着排出尼沃特岭、科罗拉多前岭高地地区以及南落基山脉花岗岩核心邻近地区的水的溶质化学成分。本研究中采样的 37 个泉水中的水以通常较短的陡峭路径（约 0.3 公里）流过浅层风化层，平均渡越时间 (MTT) 为数周至数月，产生以 Si、Ca2+、Na+ 和 HCO3− 为主的溶液，局部为 SO42−。岩石类型对泉水、地表水和浅层地下水化学具有重要控制作用，斜长石（寡长石）是溶解的 Na+ 和 Si 的主要来源。 Ca2+ 浓度超出寡长石风化化学计量预测约 3.5 倍；过量的 Ca2+ 可能代表风成物质、脉状方解石或微量矿物质的风化。碱金属阳离子和硅的浓度增加缓慢，Niwot Ridge 泉水的 MTT 估计为 0.2 年，井采样的浅层地下水的 MTT 为数年。硅酸盐矿物的化学风化速度很慢，对于寡长石和微斜长石，估计速率分别约为 2.0 和 0.2 pmol·m−2·s−1；矿化程度最高的泉水仅含有高岭石和蒙脱石。在奥罗德尔 (Orodell) 的博尔德溪 (下游约 25 公里) 测量到的溶解碱离子 + Si 中，有超过 50% 在水从尼沃特山脊的高山泉水涌出之前积累。全球气温变暖正在将更多的高海拔降水转变为降雨，可能会改变径流模式、运输时间和溶质负荷。因此，高山水域获取溶质的影响远远超出了小型高地流域。
Snowmelt‐fed springs and small (0.5 km2) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca2+, Na+, and HCO3−, locally SO42−. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na+ and Si. Concentrations of Ca2+ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca2+ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m−2·s−1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments.